Graphical Interface DesignYour best bet may be to look for general advice guidelines on flash and/or website design and work from there. Game interfaces aren't that far removed from any other sort of UI graphic design. Unfortunately graphic design is an art, not a science, and ultimately its going to be that well-known mix of inspiration and perspiration that builds what you are looking for.

XNA or SlimDX (DirectX 10) for multitouch rhythm game simulatorThe explanation I have heard that XNA Touch API doesn't support Windows is that Windows Multitouch API works quite differently than Zune/WinPhone 7 (fewer HW differences, simpler APIs), and Zune/WP7 was the priority for XNA. The Windows 7 Touch API is linked in my answer and will be equally hard to work with in XNA and SlimDX, so you may want to pick the one you prefer to work with or know better. Here's an example I found in Google for using XNA with Windows 7 multitouch: xna-uk.net/blogs/randomchaos/archive/2010/02/10/…

Zooming and panning a camera simultaneously causes a swooping effectAt first glance I don't see anything obvious. My first check would be that order of operations matter with Matrix multiplication and simply re-ordering the operations could be a starting point to try. I'd try moving the Scale first. Also I think you can just use the scalar Scale * Matrix.Identity rather than needing CreateScale. On the other hand, you could probably just use the CreateScale entirely instead of Matrix.Identity.